Some focus on the anonymous quote, “be careful what you wish for,” from the Tale of the Monkey’s Paw, by W.W. Jacobs, published in 1902, but the use is clearly much older, and probably untraceable. The context and meaning varies.

While I don’t have the original cite yet, Goethe (1749 – 1832) has been paraphrased or quoted as saying:

“Beware of what you wish for in youth, because you will get it in middle life.”

“be careful what you wish for, because if you wish hard enough you are pretty sure to get it.”

Betty Leicester’s English Christmas, by Sarah Orne Jewett, in St. Nicholas: a monthly magazine for boys and girls, Volume 23, Part 1. 1883

In 1900, Gale and Buss Newcomb used the quote “Be careful what you wish for,” in the story Someone to Crawl Back to.

In 1937, there was:

“Be careful what you wish for because you are liable to get it,” she thought with a delicious anticipatory shudder.From these beginnings, 1937, by Jane Annixter. page 173.

C. Joseph Touhill, Gregory Touhill and Thomas O’Riordan, like many others, attribute the quote to a Chinese proverb.

“Be careful what you wish for, lest it come true.” The origin of this famous quote is fuzzy and frequently attributed to an old Chinese proverb, but most people agree that it sums up an important lesson in life.Commericalization of innovative technologies: bringing good ideas to the marketplace, 2008.

I have not yet seen any actual Chinese proverb that use this quote.

A search of Google Books before 1950 does not find a single instance of the quote being attributed to a Chinese proverb. The more common reference is to Goethe, to unidentified wise men, or the common advice of mothers or grandmothers to young children.

In a 1958 textbook for elementary school reading, Paul Paul Andrew Witty asked:

Why did the author quote the Chinese proverb: “Be careful what you wish for; you are apt to get it”?Reading roundup, Volume 1‎ – Page 45

Google books does not attribute the quote to a Chinese proverb again until 1975, in Deathbird stories: a Pantheon of modern gods By Harlan Ellison. The quote would be attributed to a Chinese proverb 14 times in the 1980s, 67 times in the 1990s, and 306 times in the past decade, according to a June 13, 2010 text search on Google Books.

There are similar phrases found in French folk tales, and undoubtedly in other languages and cultures.

For 1981 to the present, The New York Times archives has 161 hits for the phrase, “be careful what you wish.”

A search for the phrase in Google scholar gives more than 3,400 hits.
Google blogs gives 950k hits.
Google’s web search gives more than 6 million hits.

The phrase is also used in a number of popular songs, including this one by Jonatha Brooke.